All terrain vehicles (ATV's) have become very popular for both recreational and utility purposes. ATV's are off-road vehicles characterized by having four wheels (two front and two rear) with low pressure tires, handlebars connected to the front wheels for steering, a straddle-type seat designed for a single rider, laterally extending footrests on opposite sides of the vehicle, and an engine and transmission located generally beneath the straddle-type seat and substantially between the footrests. Typically ATV's are not wider than about 50 inches-most commonly about 44-48 inches in overall width. The transmission typically is connected by a suitable drive train to the rear wheels. In many applications, it is desirable to have all four wheels driven by the engine. Four wheel drive ATV's typically have one drive train connecting the transmission to the rear wheels and a separate drive train connecting the transmission to the front wheels.
ATV's desirably include a braking system capable of braking all four wheels. Typically the braking system includes a separate disc brake on each front wheel and a disc brake on the generally rigid axle carrying the rear wheels (though on ATV's having the rear wheels mounted on independent suspensions, separate brake units may be provided for each rear wheel). A master cylinder, typically operated by a handlebar-mounted lever, is hydraulically connected to each of the disc brake calipers so that actuation of the lever simultaneously actuates all of the brake calipers, providing even braking of all of the ATV's wheels.
In some circumstances, however, it is desirable to permit actuation of the rear brakes without actuating the front brakes. For this purpose another brake lever--hand or foot actuated--is connected through a mechanical linkage (such as a cable) to the rear brake caliper. This mechanical linkage therefore bypasses the hydraulic system -;while permitting the rear brakes to be applied independent of the front brakes.
Because mechanical linkages typically require periodic adjustment as the brake pads wear, however, some manufacturers have utilized a second, separate rear caliper on the rear brake rotor, the second caliper being actuated by a second brake lever. The introduction of an additional caliper, however, adds significant cost to the braking system, as well as additional weight to the vehicle.